1. Field of the Invention
The present invention relates to a short pumping stem for flat display screens, more particularly for microtip screens.
The invention generally relates to the field of flat display screens constituted by a vacuum chamber, and more particularly to microtip screens, made from two thin glass plates, the back plate, or cathode plate, including a matrix array of electron emitting microtips, and the front plate, or anode plate, being coated with a transparent conductive layer bearing phosphor elements.
2. Discussion of the Related Art
Such microtip screens are usually manufactured according to the following steps: conventionally depositing onto two glass plates the various elements constituting the cathode and the anode; assembling the two plates so as to face each other in their respective definitive position, with interposition of a sealing fusible joint at their periphery to form a vacuum chamber; generating a vacuum and maintaining it in the chamber while the latter is heated for degassing the components; and cooling the chamber.
The last phase requires the provision, on one of the plates, of an exhaust tube, or pumping stem, to which an exhaust pipe is connected. The pumping stem is in turn closed once a vacuum and degassing are achieved, but an external protuberance still remains, which increases the thickness of the manufactured device. In addition, the pumping stem renders the plate on which it is positioned more fragile; so, particular care is required to handle and to store the plate and the screen.
The elements contained in any vacuum electron tube diffuse varying quantities of gases inside the chamber. The presence of these gases significantly impairs the operation of the vacuum tube, more particularly in the case of flat display screens which include active elements of very low size and which are separated by extremely short distances. This spurious degassing increases the pressure in the chamber which is detrimental for the correct operation of the screen and may cause the screen to be inactive despite the presence of a gas trap generally constituted by a getter for adsorption of the diffused gas. This getter is generally formed by a prefabricated element generally made of a barium-aluminum alloy, in the form of a plate, a strip or a bar, which is introduced into the chamber before a vacuum is generated. However, the small space available in flat display screens does not allow the use of elements having a sufficient surface to prevent them from saturating, which occurs after a determined service time. So, the getter is generally positioned in the pumping stem which, accordingly, must have a non-negligible length.